Preparing garden for next season
Thanks for writing. Fall tilling can be a good idea as it gives you a headstart on spring and can disrupt the life cycle of some pests and diseases, helping you have a healthy garden next year.
As far as the black plastic goes, I don't see any good reason to put that over your soil for winter. If you did want to add something, I'd incorporate some compost.
---Justin, Senior Garden Editor, BHG.com